A power generator such as, for example, a solar power generation system in which electric power generated by a solar panel is used in a house or the like includes a DC voltage bus (hereinafter an “HVDC bus”). A photovoltaic (hereinafter “PV”) converter, an inverter, a bidirectional DC-DC converter, and the like are connected to the HVDC bus. The PV converter outputs electric power generated by a solar power generation apparatus to the HVDC bus with a predetermined voltage. The bidirectional DC-DC converter to which a secondary battery is connected converts a DC voltage transferred/received between the secondary battery and the HVDC bus to a predetermined constant voltage. Furthermore, the inverter transmits the electric power generated by the power generator or the electric power stored in the secondary battery to an electric power system, and supplies electric power from the electric power system to the HVDC bus.
Patent Document 1 (identified below), for example, discloses a power supply system, in which a plurality of power supply units are connected to a DC voltage bus that is capable of performing cooperative control. The power supply system disclosed in Patent Document 1, in which a plurality of power supply units such as a solar power generation unit or the like are connected to the DC voltage bus, autonomously determines a transfer/reception amount of electric power transferred/received with the DC voltage bus on the basis of a voltage of the DC voltage bus. It is noted that the above-described solar power generation system generally includes a detection circuit for detecting the voltage of the HVDC bus in order to maintain the voltage of the HVDC bus at a predetermined value and controls the voltage by switching control or the like such that the detection result becomes the predetermined voltage.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-224009.
In general, it is expected that the solar power generation system or the like will be used for a long period. However, an error (deviation) may occur in the detection result of the voltage by the detection circuit described above during the long-term use. For example, in Patent Document 1, the detection voltage of each of the power supply units varies with respect to a true value of the voltage of the HVDC bus. As a result, there is a risk that the voltage of the DC voltage bus does not stabilize.
In other words, because the values of the detection voltages detected by the respective power supply units are different, it is difficult to stably control the HVDC bus voltage. Accordingly, countermeasures against the error in the detection circuit caused by the long-term use are needed. Additionally, when a higher voltage than a desired voltage value (for example 380 V) is continuously applied to each component such as a PV converter or the like connected to the HVDC bus, there is a problem that a lifespan thereof shortens. Accordingly, the voltage of the DC voltage bus is desirably set so as to be maintained at a lower voltage value while being close to the desired voltage value as much as possible.